A device to control air inflow to an engine of a car and the like includes a throttle valve device. FIG. 6 is a schematic view showing one example of the throttle valve device. Referring to FIG. 6, a throttle valve device 91 comprises a throttle body 94 forming an air inlet path in its inside, a throttle blade 95 adjusting an air inlet amount by opening and closing, a throttle shaft 93 to fix the throttle blade 95, and a shell-type roller bearing 92 to support the throttle shaft 93 rotatably. Here, the shell-type roller bearing 92 is used as a bearing to support the throttle shaft 93 because an outer diameter of the bearing is smaller than that of a ball bearing and the like, and a seal having high sealing properties can be assembled in, so that it has air leak protection performance.
The throttle valve device 91 opens and closes the throttle blade 95 by rotating the throttle shaft 93 by a wire or a motor (not shown) through a gear to adjust the air inlet amount. The shell-type roller bearing 92 is pressed into an inner diameter hole provided in the throttle body 94 and fixed.
Here, the above shell-type roller bearing for supporting the throttle shaft comprises a seal to prevent leakage of air between the bearing and the throttle shaft.
FIG. 7 is a sectional view showing a part of a conventional cored seal assembled in a shell-type roller bearing in a free state. In FIG. 7, an outer diameter surface of a throttle shaft (not shown) positioned on the inner diameter side of the cored seal for being assembled in the shell-type roller bearing is shown by a two-dot chain line. In addition, the term “free state” in this specification means a state in which the seal is not assembled between the throttle shaft and the shell-type roller bearing. Referring to FIG. 7, a cored seal 101 for being assembled in a shell-type roller bearing comprises an elastic annular member 102 and a cored bar 103 comprising a metal member. Since the cored seal for being assembled in the shell-type roller bearing comprises the cored bar 103, it can ensure rigidity and in addition, its thermal shrinkage is small even at low temperature.
An outer diameter X of the cored seal 101 for being assembled in the shell-type roller bearing is provided by adding interference 2Y to an inner diameter C of a shell-type outer ring to be assembled. Since the interference Y is provided, when the cored seal 101 for being assembled in the shell-type roller bearing is pressed into an inner diameter hole, its outer diameter surface 104 can be in contact with an inner diameter surface of the inner diameter hole so as to nip it with appropriate pressure, so that leakage between the cored seal 101 for being assembled in the shell-type roller bearing and the shell-type roller bearing can be prevented. In addition, the cored seal 101 for being assembled in the shell-type roller bearing comprises a lip part 105 projecting toward the inner diameter side. An inner diameter Z of the lip part 105 is designed so as to be smaller than an outer diameter E of the throttle shaft. Thus, when the cored seal is mounted on the throttle shaft, the lip part 105 nips the outer diameter surface of the throttle shaft with appropriate pressure and leakage between the cored seal 101 for being assembled in the shell-type roller bearing and the throttle shaft can be prevented.
Next, a description will be made of a case where the cored seal 101 for being assembled in the shell-type roller bearing is assembled in a shell-type roller bearing. FIG. 8 is a sectional view showing a shell-type roller bearing 111 comprising the cored seal 101 for being assembled in the shell-type roller bearing, in which the cored seal 101 for being assembled in the shell-type roller bearing in the free state before assembled is shown by a dotted line. Referring to FIG. 8, the shell-type roller bearing 111 comprises a shell-type outer ring 112, a plurality of rollers 113, a retainer 114, and the cored seal 101 for being assembled in the shell-type roller bearing. The cored seal 101 for being assembled in the shell-type roller bearing is assembled between the shell-type outer ring 112 and a throttle shaft. Here, since an inner diameter surface 115 of the shell-type outer ring 112 nips an outer diameter surface 104 of the cored seal 101 for being assembled in the shell-type roller bearing, and an outer diameter surface of the throttle shaft nips the lip part 105 with appropriate pressure, leakage is not generated between the shell-type outer ring 112 and the throttle shaft.
However, since the cored seal 101 for being assembled in the shell-type roller bearing comprises a plurality of members, its cost becomes high. In addition, since the cored seal 101 for being assembled in the shell-type roller bearing has rigidity, it is difficult to remove it after assembled in the shell-type roller bearing.
In view of the above problem, a coreless seal assembled in a shell-type roller bearing and comprising no cored bar is disclosed in Japanese Unexamined Patent Publication No. 2004-293618. According to the Japanese Unexamined Patent Publication No. 2004-293618, since the coreless seal for being assembled in a shell-type roller bearing only comprises an elastic member, its cost is low and it can be easily removed after assembled in the shell-type roller bearing.
Here, a coreless seal for being assembled in a shell-type roller bearing will be described. FIG. 9 is a sectional view showing a part of the coreless seal for being assembled in the shell-type roller bearing. Referring to FIG. 9, a coreless seal 106 for being assembled in a shell-type roller bearing comprises an elastic annular member 107 only. The dimension of the coreless seal 106 for being assembled in the shell-type roller bearing is the same as that of the cored seal 101 for being assembled in the shell-type roller bearing described above such that an outer diameter X is provided by adding the interference 2Y to an inner diameter C of an inner diameter hole, and an inner diameter Z of a lip part 108 is designed so as to be smaller than an outer diameter E of a throttle shaft.
According to the coreless seal 106 for being assembled in the shell-type roller bearing comprising only the elastic member, similar to the cored seal 101 for being assembled in the shell-type roller bearing as described above, when it is assembled between a shell-type outer ring and the throttle shaft, leakage between them can be prevented at room temperature. However, the coreless seal 106 for being assembled in the shell-type roller bearing does not have the above dimensional relation at low temperature, so that leakage between them cannot be prevented.
This will be described with reference to FIG. 10. FIG. 10 is a sectional view showing a part of the coreless seal 106 assembled in the shell-type roller bearing 111 at low temperature. In addition, the coreless seal 106 for being assembled in the shell-type roller bearing at room temperature is shown by a dotted line. Referring to FIG. 10, since the coreless seal 106 for being assembled in the shell-type roller bearing shrinks in a direction shown by an arrow W at low temperature, its outer diameter becomes X′ from X, so that it becomes smaller than the inner diameter C of the inner diameter surface 115 of the shell-type outer ring 112. In this case, when it is assembled in the shell-type roller bearing 111, the inner diameter surface 115 of the shell-type outer ring 112 does not nip the outer diameter surface 109 of the coreless seal 106 for being assembled in the shell-type roller bearing, so that a gap V is generated between them. Thus, leakage is generated between the shell-type roller bearing 111 and the throttle shaft through the gap V.
In addition, since the lip part 108 on the inner diameter side also shrinks in the direction shown by the arrow W, the inner diameter of the lip part 108 becomes Z′ from Z, so that the lip part 108 is positioned on the more inner diameter side. In this case, a nip amount is increased and a bite amount to the throttle shaft is increased, so that the throttle shaft and the coreless seal 106 for being assembled in the shell-type roller bearing are rotated together at the time of rotation, causing sealing properties to be lowered.